1. Field of the Invention
The invention relates to a display medium using mobile fine particles capable of being widely used for optical elements such as a light control glass, light control element and display element, as well as to a display element and a display method.
2. Description of the Related Art
With the progress of high information society, the need for electronic paper systems, color display systems and large area display systems is increasing. Display technologies such as CRT, liquid crystal, EL, LED and plasma displays have been developed for realizing these demands. In addition to these spontaneous emission systems, development of reflection display systems has been investigated as low electric power-consuming methods with less incompatibility to human eyes. Reflection liquid crystals have been a leading technology among the reflection display systems.
While there is a great need for a next-generation electronic paper display system, no promising technologies have been established so far. Electrophoresis methods, liquid crystal methods and organic EL methods have been considered as candidate methods. Since the liquid crystal method uses a filter method, reduction in thickness and weight of the medium is difficult. Since the organic EL method relies on spontaneous emission with no memory capability, the application range of this method is restricted.
Disclosed technologies for a display element using the electrophoresis method are as follows. For example, Japanese Patent Application Laid-Open (JP-A) No. 64-86116 discloses a method for delivering microcapsules, in which a dispersion medium and electrophoresis particles are sealed, between a pair of electrodes. JP-A No. 4-199085 describes a magnetophoresis method using microcapsules incorporating a magnetic fluid. Furthermore, U.S. Pat. No. 6,017,584 discloses a method for disposing a mixture of a plurality of colored particles in the same microcapsule and selectively driving these particles.
However, fine dot display and full color display have been impossible in any of these methods due to the use of microcapsules. The maximum number of colors that can be simultaneously displayed in JP-A No. 64-86116 is 2 colors, and multi-color display is impossible. In addition, it has been difficult in principle to selectively drive the particles in U.S. Pat. No. 6,017,584.
JP-A No. 2000-322004 discloses technology in which approximately the same amount of charged mobile particles are disposed in a plurality of segments that have been partitioned along the surfaces of a pair of substrates disposed at a given distance apart, and a dispersion medium is colored blue while charged mobile particles are colored black, in order to improve the quality of display.
However, full color display is also difficult in this construction, and the apparatus becomes complicated since the segments need to be parallel because color reproduction by subtractive mixture of colors by a combination of particles in each layer is impossible when the segments are laminated.
While JP-A 2000-35598 discloses a method in which cells or microcapsules for displaying colors are arranged in parallel for color display, high resolution as well as sufficient contrast cannot be obtained due to the parallel arrangement. Further, while JP-A No. 2002-333643 discloses a method in which at least two layers of electrophoresis parts containing light permeable particles/medium are laminated in the vertical direction, sufficient color density cannot be obtained since dyes are used for coloring the particles.
While JP-A No. 2002-162649 disclosed a method in which a plurality of housing parts for housing fine particles after electrophoresis are provided, reproducibility of colors is poor, and thus the method fails to obtain high contrast since particles having different colors must be disposed in parallel for color display.